This invention relates to color picture tubes of the type having a mask attached to a frame which is suspended in relation to a cathodoluminescent screen, and particularly to a temperature compensating support for suspending the mask-frame assembly within the tube.
In these color picture tubes, the accuracy with which the electron beams strike the individual elemental cathodoluminescent screen areas depends, to a great degree, upon the accuracy with which the mask apertures are aligned with the elemental screen areas during operation of the tube. Thus, should the mask expand by reason of thermal effects occasioned by the impact thereon of the electron beams, the resulting misalignment of the mask apertures and elemental screen areas may cause a portion of the electron beams to impinge upon elemental screen areas other than the ones upon which they were intended to impinge.
Several methods or means have been proposed to compensate for thermal expansion of the mask by causing the mask to move (axially) toward the screen as it expands outwardly, to maintain the desired alignment of the mask apertures and elemental screen areas. One early approach disclosed in U.S. Pat. No. 2,795,719, issued to Morrell on June 11, 1957, proposed movably mounting the mask within the envelope by means of three carriages attached to the periphery of the mask and sliding on inclined tracks mounted on the envelope. Another early approach disclosed in U.S. Pat. No. 2,795,718, issued to van Hekken et al. on June 11, 1957, proposed the use of a multiplicity of flexible hinges connecting the masking member with a supporting frame, or a pivoted bell crank having arms slidably engaging the mask. These compensating means were designed primarily for use with circular masks in round tubes of moderate size and moderate deflection angle.
Most present day color picture tubes utilize a bimetallic mask mounting assembly such as described in U.S. Pat. No. 3,803,436, issued to Morrell on Apr. 9, 1974. In this patent, a bimetallic element is connected between a stud embedded in the faceplate panel and the mask electrode. The bimetallic element may be a spring welded directly to the frame or an intermediate member located between the spring and frame.
Although the bimetallic elements have served well for their intended purpose, their additional cost is relatively high. Therefore, there is a need for further development of thermal compensating mask supports which do not utilize bimetallic elements and which are not mechanically complex.